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Passive Muscle Length Changes Affect Twitch Potentiation in Power Athletes.
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.ORCID iD: 0000-0002-8580-6518
Swedish School of Sport and Health Sciences, GIH, Department of Sport and Health Sciences, Laboratory for Biomechanics and Motor Control.ORCID iD: 0000-0002-7879-9188
2014 (English)In: Medicine & Science in Sports & Exercise, ISSN 0195-9131, E-ISSN 1530-0315, Vol. 46, no 7, 1334-1342 p.Article in journal (Refereed) Published
Abstract [en]

INTRODUCTION: A conditioning maximal voluntary muscle action (MVC) has been shown to induce post-activation potentiation, i.e. improved contractile muscle properties, when muscles are contracted isometrically. It is still uncertain how the contractile properties are affected during ongoing muscle length changes. The purpose of this study was to investigate the effects of a 6 s conditioning MVC on twitch properties of the plantar flexors during ongoing muscle length changes.

METHODS: Peak twitch, rate of torque development (RTD) and relaxation (RTR), rising time and half relaxation time (HRT) were measured from supramaximal twitches evoked in the plantar flexors of 11 highly trained athletes. Twitches were evoked prior to a 6 s MVC and subsequently on 8 different occasions during a 10-minute recovery, for five different modes: fast lengthening, slow lengthening, isometric, fast shortening and slow shortening of the plantar flexors.

RESULTS: The magnitude and duration of effects from the conditioning MVC were significantly different between modes. Peak twitch, RTD and RTR significantly increased for all modes but more so for twitches evoked during fast and slow shortening as compared to lengthening. Rising time was reduced in the lengthening modes, but slightly prolonged in the shortening modes. HRT was significantly reduced for all modes except fast lengthening.

CONCLUSION: The findings show that the effects of a conditioning MVC on twitch contractile properties are dependent on direction and velocity of ongoing muscle length changes. This may imply that functional enhancements from a conditioning MVC might be expected to be greatest for concentric muscle actions, but are still present in isometric and eccentric parts of a movement.

Place, publisher, year, edition, pages
2014. Vol. 46, no 7, 1334-1342 p.
National Category
Sport and Fitness Sciences
Research subject
Medicine/Technology
Identifiers
URN: urn:nbn:se:gih:diva-3193DOI: 10.1249/MSS.0000000000000245PubMedID: 24389516OAI: oai:DiVA.org:gih-3193DiVA: diva2:686978
Funder
Swedish National Centre for Research in Sports
Available from: 2014-01-13 Created: 2014-01-13 Last updated: 2016-04-01Bibliographically approved
In thesis
1. Post activation potentiation: Modulating factors and mechanisms for muscle performance
Open this publication in new window or tab >>Post activation potentiation: Modulating factors and mechanisms for muscle performance
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Introduction: Acute enhancements of muscle contractile properties and performance subsequent to a maximal or near maximal conditioning contraction are often termed post activation potentiation (PAP). Although still controversial, PAP is commonly linked to enhancements in the myosin regulatory light chain phosphorylation, leading to improvements in the excitation–contraction coupling. The PAP seen after a conditioning task often coexists with fatigue and is known to depend on strength level, muscle fiber type and age. Less is known about how factors such as static and dynamic changes in muscle length affect PAP, and on the relative contribution of contractile and tensile components to PAP.

Aim: To enhance our understanding of how, and under what conditions, a single maximal isometric contraction affects plantar flexor muscle contractile performance, and other muscle tendon properties, in power athletes.

Methods: Supramaximal twitches were evoked via electrical stimulation of the tibial nerve of athletes before and on several occasions after a 6-second maximal voluntary isometric contraction (6-s MVIC) in both static muscle, and during passive muscle lengthening and shorting at different angular velocities. Several contractile variables were measured from the twitches. The effects of a 6-s MVIC on Achilles tendon stiffness was calculated from torque and ultrasonography based measurements of tendon length at two submaximal contraction intensities. Overall stiffness index was calculated by analyzing the passive lengthening torque/angle curve.Results: A single MVIC enhanced muscle contractile properties and electromechanical delay for up to 5 minutes. Plantar flexor twitch variables such as peak twitch, rate of torque development and rate of torque relaxation were enhanced during shortening compared to lengthening muscle actions, and in an extended as compared to a flexed knee position. Achilles tendon stiffness and overall stiffness index were not significantly modulated by a single 6-s MVIC.

Conclusion: The results of this thesis imply that functional enhancements from a 6-s conditioning MVIC would mainly come from improvements in contractile rather than tensile components. Stiffness changes should be monitored in future PAP-related studies since they may still occur after more extensive conditioning protocols than the current one. Improvements in contractile components subserving muscle strength after a conditioning MVIC suggests that enhancements in muscle power after a conditioning task should be greatest in fast concentric muscle actions, though still present in muscle lengthening. Conditioning should be performed in a position where full activation is easy to achieve and tailored to mach an athlete or group of athlete’s current status and characteristics, maximizing performance in a specific sport event.

Place, publisher, year, edition, pages
Stockholm: Gymnastik och idrottshögskolan, GIH, 2016. 53 p.
Series
Avhandlingsserie för Gymnastik- och idrottshögskolan, 04
Keyword
Potentiation, twitch, triceps surae, knee angle, stiffnes, length changes, electromechanical delay
National Category
Sport and Fitness Sciences
Research subject
Medicine/Technology
Identifiers
urn:nbn:se:gih:diva-4280 (URN)978-91-980862-4-9 (ISBN)
Public defence
2016-02-02, Aulan, Gymnastik- och idrottshögskolan, Lidingövägen 1, Stockholm, 12:30 (English)
Opponent
Supervisors
Projects
Doctoral project: Post activation potentiation - Modulating factors and mechanisms for muscle performance.
Note

The project recived financial support from the Swedish National Centre for Research in Sports (CIF). Paulo Gago also wishes to thank the Fundação para a Ciência e Tecnologia (FCT), Portugal for the Ph.D. Grant (SFRH/BD/103572/2014).

New version 2015-01-25 updates the previous one by correcting the errors described in the correction list file (errata).

Available from: 2016-01-07 Created: 2015-12-31 Last updated: 2016-02-11Bibliographically approved

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